How to flip without using mirror modifier
Select green object, press Shift+S and choose cursor to selected. Change pivot center for rotation/scaling to 3D cursor.Select yellow object (all meshes) and either press S,X -1 (to scale it by value of -1 on the X axis, which will cause to mirror the object to the other side) or CTRL+M,X (which will cause to mirror object to the other side)